This invention relates to semiconductor chip protection, and, more particularly, to a power supply switch circuit for detecting a ground lead in a circuit and shutting off power to the faulty circuit.
A short, or current leak, between power and ground usually renders a semiconductor circuit useless. Normally, chips which have this problem would be thrown away. However, on a Wafer Scale Integration (WSI) chip, which comprises a number of circuits on a single wafer, one does not want to discard the entire wafer merely because one circuit on the wafer fails. Also, because of the size of the circuits, the probability that some of the circuits will have a gross short between power and ground is greatly increased.
It is necessary to have a way of cutting off power to parts of the circuit where power shorts may exist without affecting other parts of the circuit. Thus, it would be possible to use the other parts of the circuit even if a power short exists in portions of the circuit.
Various protection circuits have been devised for other applications. For example, U.S. Pat. No. 4,078,200 provides a circuit that protects a device from excessive current flow caused by a short circuit. The approach involves limiting the current to the device. However, the disclosed circuit makes no attempt to shut off the current.
U.S. Pat. No. 4,463,270 detects a difference in the relative amplitudes of two voltages, but again does not shut off the current in the event of a short circuit.
U.S. Pat. No. 4,329,600 provides a protection circuit having means for limiting excessive power dissipation in its output stage. When the output buffer is turned on, if the output voltage does not reach the desired level in a certain time, then the circuit creates a power to ground short in order to shut off the output buffer. Clearly, the protection circuit does not eliminate power to ground shorts.
U.S. Pat. No. 4,353,105 provides a circuit that detects latch-up, which results in excessive current drain. The circuit turns off the chip, leaks off the excess charge, and then turns the chip back on. However, this approach does not solve the problem of dealing with a short in a section of a circuit.
Thus, there remains a need to provide a means for detecting a short in a section of a chip circuit and turning that section off permanently.